Linear voltage regulator circuit incorporating light emitting and photovoltaic devices

ABSTRACT

A linear regulator operates in the manner of a linear voltage regulator, but with the functionality of a switching converter. This concept enables DC voltage up-conversion with no switching, more efficient step down of large voltage steps, and requires no expensive and bulky additional components. An optocoupler device transfers power between light emitting and photovoltaic devices.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/728,463, filed Sep. 7, 2018, Provisional Application No. 62/800,805,filed Feb. 4, 2019, Provisional Application No. 62/800,809, filed Feb.4, 2019, and Provisional Application No. 62/824,037, filed Mar. 26,2019. The entire contents of those applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

DC-DC conversion is a very common element of a variety of circuits. Veryefficient step down (“buck”) converters and step up (“boost”) convertersare available, which use a switching technique to regulate the voltage.However, there are several drawbacks to switching DC-DC converters.Firstly, they require additional components such as inductors andcapacitors, which increase the footprint and cost of the solution. Also,high-frequency switching introduces voltage ripple, which can createproblems in noise-sensitive applications and requires additional designcomplexity to suppress. Also, switching converters are susceptible toelectromagnetic interference effects which can create a variety ofproblems in electronic circuits.

Alternative devices for DC-DC conversion are linear voltage regulators,which are less complex than switching converters, require fewer externalcomponents and there is no noise generated by switching. Therefore,these devices can be low cost, insensitive to EMI and a very compactalternative to switching converters. However, there are two maindrawbacks with linear voltage regulators. The first is that they onlystep down voltage, severely limiting the cases where the devices can beemployed. The input voltage is required to be greater than the outputvoltage by an amount known as the dropout voltage, which in low dropout(LDO) linear regulators can be as low as 50-100 mV, or as high as 2V inconventional linear voltage regulators. The second drawback is thattheir efficiency is generally lower, especially when the differencebetween input and output voltages is large. In battery operated systemsthis equates to increased battery drainage and significant amounts ofwaste heat generation.

SUMMARY OF THE INVENTION

In this invention, a device is provided that operates in the manner of alinear voltage regulator, but with the functionality of a switchingconverter. This concept enables DC voltage up-conversion with noswitching, more efficient step down of large voltage steps, and requiresno expensive and bulky additional components. At the heart of theinvention is an optocoupler device which transfers power between lightemitting and photovoltaic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a linear voltage regulator having anoptocoupler section in accordance with one embodiment of the invention;

FIG. 2 is a low-dropout voltage regulator having an optocoupler section;

FIG. 3 is an alternative configuration having an LED andphototransistor;

FIG. 4 is a circuit diagram of FIG. 3 with a second transistor;

FIG. 5 is a circuit diagram with the second transistor connected to thephotovoltaic devices;

FIG. 6 is a circuit diagram having a linear regulator connected betweenthe second transistor and the output;

FIGS. 7(a), 7(b) show a voltage reducing optocoupler device;

FIGS. 8(a), 8(b) show a voltage reducing optocoupler device havingmultiple photovoltaic regions and blocking regions;

FIGS. 9(a) 9(b) show a voltage reducing optocoupler device with multiplelight emitting regions stacked vertically;

FIGS. 10(a), 10(b) show a voltage reducing optocoupler device having thelight emitting region on the bottom and the photovoltaic regions on top;

FIGS. 11(a), 11(b) show a voltage reducing optocoupler device withmultiple light emitting regions on the bottom and the photovoltaicregions on top;

FIGS. 12(a), 12(b) show a voltage reducing optocoupler device withmultiple photovoltaic regions stacked vertically;

FIGS. 13, 14 show voltage reducing optocoupler devices having ahorizontal side-by-side configuration; and

FIGS. 15-17 show voltage reducing optocoupler device assemblies.

DETAILED DESCRIPTION OF THE INVENTION

In describing the illustrative, non-limiting embodiments of theinvention illustrated in the drawings, specific terminology will beresorted to for the sake of clarity. However, the invention is notintended to be limited to the specific terms so selected, and it is tobe understood that each specific term includes all technical equivalentsthat operate in similar manner to accomplish a similar purpose. Severalembodiments of the invention are described for illustrative purposes, itbeing understood that the invention may be embodied in other forms notspecifically shown in the drawings.

A standard linear voltage regulator operates by taking an unregulatedinput, V_(in), and producing a regulated output, V_(out). The regulationis achieved by a variable voltage drop across a transistor connected tothe output. The transistor is controlled by an error amplifier whichcompares the output voltage to a voltage reference, V_(ref). In thiscircuit, V_(out) is always lower than V_(in). Very low dropout voltagescan be achieved by modifying this basic circuit to use a common emitteroutput stage as described, for example, in Horowitz & Hill “The Art ofElectronics”.

Turning to the drawings, FIG. 1 shows one illustrative, non-limitingembodiment of the improved linear voltage regulator circuit 100 of theinvention. The circuit 100 includes a transistor 1, an amplifier 5, andan optocoupler section 102. The optocoupler section 102 has a lightemitting section 104 comprising an array of LEDs 8, and a photovoltaicsection 106 comprising an array of photovoltaic devices 9. Thephotovoltaic device 9 can be any suitable devices, for example aphotosensor, photodetector, solar cell, or a semiconductor junction(e.g., p-n junction) that has an anode and cathode contact and absorbsexternal photons above the bandgap of the lowest bandgap material in thedevice, which can be extracted as electrical current in an externalcircuit.

The transistor 1 is not connected to the output, as in a conventionalvoltage regulator, but rather to one or more light emitting diodes 8connected in a combination of series or parallel connected strings. Thecircuit has a transistor 1 connected to an input terminal 1 with anunregulated voltage. The circuit is shown with a npn bipolar junctiontransistor, but analogous operation could be achieved using other typesof transistor, such as a MOSFET. The function of the circuit is toproduce a regulated voltage output at the output terminal 3.

A third terminal 4 provides a voltage reference, which may be anexternal voltage source, a suitable diode or other similar component forproviding a voltage reference. The voltage drop across transistor 1 iscontrolled by an error amplifier 5 which compares the voltage at theoutput terminal 3 through a potential divider, formed by resistors 6 and7, with the voltage reference at the reference terminal 4. The erroramplifier 5, when in a feedback loop, generates a voltage whichstabilizes the output voltage and minimizes the difference between thereference and the feedback voltage.

Thus, in the embodiment shown, the amplifier has a first input connectedto the voltage reference 4, and a second input connected to the outputterminal 3 through the potential divider. Specifically, the first andsecond resistors 6, 7 of the voltage divider are connected in serieswith the second input of the amplifier 5 connected therebetween. Thefirst resistor 6 has a first end that is connected to the outputterminal 3 and a second end that is connected to a first end of thesecond resistor 7. The second end of the second resistor 7 is connectedto ground. The second input to the amplifier 5 is connected to thesecond end of the first resistor 6 and the first end of the secondresistor 7.

The potential divider provides the feedback voltage which is compared tothe reference voltage in the amplifier. The feedback voltage is afraction of the output voltage, controlled by the resistors' values,thereby controlling the regulated voltage output. By changing the valuesof these resistors, the voltage regulator can be modified to producedifferent output voltages (some designs of regulator ICs requireseparate resistors to be connected off the chip, others have theresistors built-in to the IC). Using a variable resistor as one or bothof the resistors in the divider is an easy way to make a variablevoltage regulator.

The output from the amplifier 5 is connected to the base of thetransistor 1, and the collector of the transistor is connected to theinput terminal 2. The connection between the voltage reference 4 and theinput terminal 2 is optional and depends on the type of voltagereference being used. If the voltage reference is a diode then the diodeis connected to the input 2 through a resistor. If an external reference(e.g. power supply) is used as a reference, terminal 4 does not have tobe connected to the input terminal 2.

In addition, the emitter of the transistor 1 is connected to a lightemitting section 104. The light emitting section 104 is an array of oneor more light emitting diodes (LEDs) 8 which are connected in anycombination of series and parallel interconnections. The light emittersection 104 example shown in FIG. 1 has four LED devices 8 connected inparallel. The LEDs 8 transmit photons to a photovoltaic section 106,which is an array of one or more photovoltaic (PV) devices 9 connectedin a combination of series or parallel strings. The direction of photontransfer follows the arrow shown by 10, and therefore the bandgap energyof the PV devices is required to be equal to or less than the energy ofphotons emitted by the LED devices—but only the narrowest bandgap partof the PV device is needed to have a bandgap equal to or less than theemission energy of the LED. For example, the PV device may comprise aheterojunction having a wide bandgap n region and a narrower bandgap pregion. A PV device 9 is aligned with a respective LED 8 to receive anddetect light emitted from the LED 8. The LEDs 8 emit a light in responseto a signal received from the emitter of the transistor 1.

The transistor 1 provides a fraction of the input voltage to the LEDs 8,controlled by the amplifier feedback loop. The intensity and wavelengthof the light from each LED 8 is substantially the same, although seriesresistance and real-world variations in LEDs make that an approximation.The fraction of the input voltage 2 not passed to the LED) 8 array isgiven up as heat in the transistor 1. The output from the last PV device9 in the series connects to the output terminal 3.

The PV section 106 has four PV devices 9 connected in series. The LEDand PV devices may be separate components, or monolithic devices withhigh impedance between the terminals of the LED and PV sections. The PVsection is connected to the output terminal 3. There is no requirementfor the number and performance attributes of the LED and PV devices intheir respective strings to be identical. For example, it is possiblethat one large LED device 8 could pass photons to several smaller PVdevices 9, or conversely, one large PV device 9 could absorb photonsfrom several smaller LEDs 8. By using different combinations of seriesand parallel connections of the LED 8 and PV devices 9, step-up orstep-down voltage conversion is possible with this scheme.

For simplicity, no additional circuit elements for overcurrentprotection or stability are shown in FIG. 1. A variety of capacitors,resistors and transistors may be added to the circuit to improvestability and protect against short circuits, but do not govern thebasic operating principle of the regulator device. The voltage producedacross the terminals of the PV section 106 provides a voltage boost atthe output of the optocoupler section 102 relative to the input of theoptocoupler section 102. For example, the voltage across the PV section106 is greater by a factor of roughly 4× relative to the voltage acrossthe LED section when the bandgap energies of the LED 8 and PV devices 9are very similar.

More specifically, photovoltaic devices in series add their voltages,analogous to connecting batteries in series. Thus, for example, consider4 LEDs in parallel and 4 PV devices in series where the PV and LEDbandgaps are very similar and the LED luminescence is coupled to the PVdevices. Neglecting optical and electrical losses for the simplicity ofthis example, the voltage produced by the PV array will be roughly 4×greater than the voltage input to the LED array, whereas the currentproduced by the PV array will be roughly 4× smaller than the currentinput to the LED array, thereby ensuring the output power from the PVarray cannot exceed the power input to the LED array. In practice,electrical and optical losses will reduce the voltage boost to less than4× and reduce the current output of the PV array to less than ¼ of theLED input, resulting in significantly less than unity power transferefficiency of the optocoupler, where power transfer efficiency has beendefined as the output power from the PV array as a fraction of the inputpower to the LED array.

In general, the design of the LED section 104 and PV section 106 aredesigned such that the output voltage is close to the maximum powervoltage of the PV section 106 under typical operating voltage ranges,which provides the highest efficiency of electrical power out of the PVsection 106 per incident light power.

The linear regulator 100 has a feedback loop that regulates the voltage.The voltage reference 4 is compared to the voltage across the potentialdivider. The amplifier 5 minimizes the difference between the referencevoltage 4 and the feedback voltage, by controlling the voltage dropacross the transistor 1. The optocoupler section or device 102 providesadditional voltage reduction or voltage boost between the input andoutput sides, which enables either voltage upconversion, or moreefficient voltage down conversion.

In FIG. 1, all the power is transferred between the light emitter andthe PV devices. The efficiency of the optocoupler is less than unity, soif there were no voltage boosting or voltage reduction going on in theoptocoupler section 102, therefore comparable to a conventional voltageregulator, the efficiency would be lower using the optocoupler. However,when stepping down large voltage steps, reducing voltage in theoptocoupler section enables a higher efficiency than a conventionallinear regulator where the entire voltage difference is dissipated asheat in the transistor 1. Furthermore, by employing an optocoupler whichenables voltage boosting, DC-DC upconversion can be achieved using adevice which retains the advantages of a linear regulator in simplicity,low EMI and low voltage ripple.

In FIG. 2, is a low dropout voltage regulator with an optocouplersection. It is a similar configuration to FIG. 1 to provide to connectLEDs and PV devices into voltage regulator circuits which are lowdropout regulator circuits. Here, the circuit has an input terminal 2with an unregulated voltage and produces a regulated voltage at theoutput terminal 3. As in FIG. 1, a third terminal 4 provides a voltagereference. The voltage drop between the input terminal 2 and the lightemitting section 8 is now across a transistor 11 in a common emitterconfiguration, which in this example uses a pup bipolar junctiontransistor. The emitter of the transistor 11 is connected to the inputterminal 2, and the collector is connected to the LED section. The baseof the transistor 11 is connected to the emitter of a second transistor12 having a collector connected to ground. The second transistor 12 hasa base that is connected to and controlled by an error amplifier 5,which compares the voltage at the output terminal 3 through a potentialdivider formed by resistors 6 and 7, with the voltage reference at thereference terminal 4, as in FIG. 1. It provides lower parasitic voltageloss in the transistor, so that the output voltage can be closer to theinput voltage.

Also analogous to the example in FIG. 1, the transistor 11 is connectedto a light emitting section, which is an array of one or more LEDs 8connected in any combination of series and parallel connections. TheLEDs 8 transmit photons to a photovoltaic section, having of one or morephotovoltaic (PV) devices 9 connected in a combination of series orparallel strings. The direction of photon transfer follows the arrowshown by 10. As in FIG. 1, for simplicity, no additional circuitelements for overcurrent protection or stability are shown. A variety ofcapacitors, resistors and transistors may be added to the circuit toimprove stability and protect against short circuits, but are notrequired to understand the basic operating principles of the regulatordevice.

For applications where the output voltage of the PV section 9 is greaterthan the input to the light emitting section 8, achieved by buildingvoltage using series connections of PV devices, linear regulators withnegative dropout voltage can be realized. In other words, thisrepresents a linear regulator device capable of DC voltage boostconversion. Alternatively, when the output voltage of the PV section 9is significantly less than the input voltage to the light emittingsection 8, for example by using multiple LED devices in series, agreater efficiency for step-down conversion of large voltage steps canbe achieved, compared to conventional linear regulators. Usingconventional regulators for large voltage reduction, all the voltagechange would be governed by the voltage drop across a transistor,leading to a significant amount of wasted power and producing heat. Inthe circuits of FIGS. 1 and 2, a fraction of the voltage drop can beachieved using the photon transfer process, thereby raising theefficiency overall.

Galvanic Isolation

FIG. 3 shows an alternative example, non-limiting design of theregulator described in FIGS. 1 and 2 can be used to create a linearvoltage regulator device which has a high degree of galvanic isolationbetween the input and output sides of the device. The circuit has aninput terminal 2 with an unregulated voltage and the function of thecircuit is to produce a regulated voltage output at the output terminal3. A third terminal 4 provides a voltage reference. Instead of atransistor, a phototransistor 13 is used to create a controlled voltagedrop. The voltage drop across the phototransistor 13 is controlled by alight source such as a control light emitting device 14 as part of anoptocoupler architecture. The control LED 14 is connected to the outputof an error amplifier 5 which compares the voltage at the outputterminal 3 through a potential divider, formed by resistors 6 and 7,with the voltage reference at the reference terminal 4, as in FIG. 1.

The phototransistor 13 has a collector that is connected to the input 2.The emitter of the phototransistor 13 is connected to a light emittingsection 8, which transmits photons to a photovoltaic section 9, entirelyanalogous to the schemes shown in FIGS. 1 and 2. Thus, in response tolight received by the control LED 14, the phototransistor 13 provides acontrol signal to the LEDs 8. The direction of photon transfer followsthe arrow shown by 10. In this embodiment, the input 2 and output 3terminals are completely galvanically isolated, with the only currentpath between the two sides being via photon transfer. Furthermore, asimilar circuit to FIG. 2 can be constructed by replacing thephototransistor output stage 13 with a common emitter output stage 11controlled by a pnp phototransistor 15, as shown in FIG. 4.

In FIG. 3, the only way current can flow from the input to the outputside is via photons (especially if the PV and LEDs are discretecomponents), which restricts the current level which can flow. Thus, itprovides galvanic isolation, which can be a useful safety devicepreventing potentially dangerous electric shocks. Another important usefor galvanic isolation is when the input and output sides of the circuithave different ground potentials.

High Efficiency Version

FIG. 5 shows another alternative example non-limiting design of theregulator used to create DC voltage conversion with high efficiency.Here, the circuit has an input terminal 2 with an unregulated voltageand produces a regulated voltage at the output terminal 3). As in FIG.1, a third terminal 4 provides a voltage reference, and the voltage dropbetween the input terminal 2 and the light emitting section 8 is acrossa transistor 11 in a common emitter configuration. The base of thetransistor 11 is connected to the emitter of a second transistor 12. Thesecond transistor 12 is controlled by an error amplifier 5 whichcompares the voltage at the output terminal 3 through a potentialdivider, formed by resistors 6 and 7, with the voltage reference at thereference terminal 4, as in FIG. 1.

Analogous to the example in FIG. 2, the transistor 11 is connected to alight emitting section 8. The LEDs transmit photons to a photovoltaicsection, having one or more photovoltaic (PV) devices 9 connected in acombination of series or parallel strings. In the example shown in FIG.5, three LEDs 8 connected in series are optically coupled to three PVdevices 9 connected in parallel. When the bandgap energies of the LEDand PV devices are similar, this configuration results in a roughly 3×reduction of the voltage across the PV section relative to the voltageacross the LED section. The direction of photon transfer follows thearrow shown by 10.

Unlike FIGS. 1-4, in the embodiment in FIG. 5 the input terminal 2 isalso connected directly to the PV section 9. By connecting one terminalof the photovoltaic string to the input, the photovoltaic action adds orsubtracts to the voltage supplied to the load. In this configuration,only a fraction of the power supplied at the input is used to drive thelight emitting section, and the overall efficiency can be significantlygreater than if all the power from the input were routed through thelight emitter section.

In the example in FIG. 5, when the input side voltage exceeds theregulated output voltage, some of the unwanted power is dissipated inthe photovoltaic section. To minimize this, another similar embodimentof the idea places a conventional linear regulator 16 in parallel withthe circuit, as shown in FIG. 6. The input terminal of the linearregulator 16 is connected to the input terminal 2 of the device and theoutput terminal of the linear regulator 16 is connected the outputterminal 3 of the device. All other aspects of the circuit are identicalto the one shown in FIG. 5. When the input voltage at the input terminal2 exceeds the input voltage threshold of the standard linear regulator16, the power is largely diverted through the conventional regulatorcircuit. This can either be controlled by a switch, for example a singlepole double throw switch 17, or by ensuring the output voltage from theconventional regulator is set to be slightly greater than the mainvoltage regulator.

The embodiments shown in FIGS. 5, 6 enable an improvement in efficiencycompared to the embodiments in FIGS. 1-4, as the power transferefficiency of the optocoupler section can be significantly less thanunity. In FIGS. 5, 6, part of the power passes directly from the input 2to the output 3, so that only part of the power passing from the inputto the output is transferred through the optocoupler region, andtherefore the impact on overall efficiency due to the less than unityoptocoupler power transfer efficiency is reduced.

Monolithic Optocoupler Design

Optocouplers are a common device in a variety of applications, andusually discrete devices for photon generation and photon absorption.Separate components increases cost and makes efficient optical couplingdifficult to achieve. Generally, optocoupler devices are used for signaltransmission and electrical isolation, not for efficient power transfer.Monolithic optical emitter/detector devices have been demonstrated whichimprove the coupling efficiency of photons. For example, U.S. Pat. No.4,275,404 to Cassiday et al. devised a device where an LED emitter ispositioned in between two photodiode devices, all made from the sameepitaxially grown layers, on an insulating substrate. The emission fromthe side of the LED section is coupled into the photodetector sections,creating an opto-isolator. Vertical optical connections have also beendemonstrated, for example by U.S. Pat. No. 5,753,928 to Krause et al.Here, a single emitter region is stacked monolithically with a detectorregion to produce a monolithic optical emitter-detector. Voltagemultiplication has also been demonstrated in devices such as the ToshibaTLP590B. Here a single discrete LED is optically coupled to aseries-connected silicon photodiode array to produce a greater voltageoutput. However, the power transfer efficiency of this device is verylow due to the highly inefficient production, transfer and electricalconversion of photons in the device.

To achieve high power transfer efficiency, a device is provided wherethe photon generation and absorption are performed by different regionsof the same monolithic device, separated by transparent, highlyresistive, monolithic isolation layers. Step-up or step-down voltageconversion is possible if the light emitting or light absorbing regionsare made up of multiple devices connected in series. High efficiencyphoton capture is enabled by using one or more high reflectivity mirrorsor a sandwiched structure, where PV regions surround a light emittingregion in monolithic stack.

FIG. 7(a) shows a schematic drawing of an example voltage reducingoptocoupler device 200 having monolithic light emitting devices 18 andmonolithic photovoltaic devices 20. Here two light emitting regions 18,for example GaAs pn junctions, are connected to a blocking region 19.The blocking region is a material layer, or combination of materiallayers, with high transparency to the light emitting sectionluminescence and high electrical resistance, for example a verticalstack of one or more AlGaAs pn junctions. The blocking region 19 allowsphotons through, but blocks electrical current, i.e., has a highelectrical resistance. The blocking region is connected to aphotovoltaic region 20. The bandgap of the lowest bandgap absorber layerin the solar cell region should be equal to or less than the bandgap ofthe light emitting section governing the peak emission wavelength.

An optional reflector 21 on the light emitting section devices functionsto improve the coupling efficiency of photons to the photovoltaic region20. This could be an epitaxially-grown reflector such as a distributedBragg reflector (DBR), or a separately deposited reflector such as adielectric DBR or metal mirror. An optional reflector 26 on thephotovoltaic region device functions to improve the absorptionprobability of photons emitted from the light emitting region 18 in thephotovoltaic region 20.

The reflectors 21, 26, photovoltaic region 20, blocking region 19, andlight emitting regions 18 each have linear flat top and bottom surfacesand can all have substantially the same length and width, though thelight emitting regions 18 can be one device or multiple separatedevices, as shown, so that the light emitting regions 18 extendsubstantially along the blocking region 19 and photovoltaic region 20.The bottom surface of the photovoltaic region is mounted on (i.e.,coupled) to the top surface of the first reflector 26, and the topsurface of the photovoltaic region 20 is coupled to the bottom surfaceof the blocking region 19. The one or more light emitting regions 18 canbe mounted (at the bottom surface of the light emitting regions 18) tothe top surface of the blocking region 19. The bottom surface of thesecond reflector(s) 21 are coupled to the top surface of the lightemitting regions 18. There can be a gap between the light emittingregions 18, as shown, or no gap. Thus, the elements are stacked in avertical configuration.

In physically separate components, there are reflection losses for lightescaping the LED, then again entering the photovoltaic. Furthermore,only light emitted within the escape cone of the LED can escape, therest is reflected back into the LED by total internal reflection. In themonolithic optocoupler of the present invention, the refractive index ofthe LED 8 and PV 9 are very similar, so the critical angle is almost 90degrees, suppressing the escape cone limitation and reflection loss.Another benefit of a monolithic device is that the LED 8 and PV devices9 are aligned in close proximity. The other typical loss is that 50% ofthe LED) light is emitted in the direction away from the PV device, butthe mirror serves to reflect that light back toward the PV device.

FIGS. 1-6 can use any suitable optocoupler device 102. In addition, theoptocoupler devices of FIGS. 7-17 can be used in any suitable circuitconfiguration, such as for example, as photovoltaic output optocouplers.One application for these is for MOSFET gate driving.

However, FIGS. 7-17 are all examples of the structure which could beused for the optocoupler section 102 of the regulators 100 shown inFIGS. 1-6. In that instance, the optocoupler device 100 of FIGS. 1-6 arerepresented as the optocoupler devices 200 of FIGS. 7-17. And, the lightemitting device 18 and PV devices 20 of FIGS. 7-17 correspond to thelight emitting devices 8 and PV devices 9 of FIGS. 1-6.

Referring to FIG. 7(b), the light emitting region 18 has two terminals22 and 23, and in this example, two light emitting devices connected inelectrical series. The photovoltaic region 20 has two terminals 24 and25, and one photovoltaic device. The photovoltaic device can be centeredand positioned between the two light emitting devices. When the bandgapenergy of the light emitting and photovoltaic devices are similar, theinput voltages between terminals 22 and 23 is roughly a factor of two ormore greater than the voltage between terminals 24 and 25. This could bean epitaxially-grown reflector such as a distributed Bragg reflector(DBR), or a separately deposited reflector such as a dielectric DBR ormetal mirror.

The example in FIG. 7 contains a single photovoltaic device large enoughto accept photons from both devices in the light emitting regions 18.Alternatively, as shown in FIGS. 8(a), 8(b), an equivalent scheme coulduse two photovoltaic devices 20 connected in parallel, one for eachlight emitting region 18, and with a respective blocking device 19. Ingeneral, a single optocoupler may have one (1) light emitting device andone (1) photovoltaic device, or any number of series or parallelconnected light emitting and photovoltaic devices with any ratio ofdevice areas.

In FIG. 8, having 1 LED and 1 PV per individual monolithic stackprovides a basic building block to get a large number of possible ratiosof voltage between LED and PV strings by connecting arbitrary numbers ofthem in any series/parallel combination, whereas FIG. 7 gives a fixed2:1 combination. However, additional metal interconnections are neededin FIG. 8 to achieve the same result as in FIG. 7, which may introducemore series resistance.

FIGS. 9(a), 9(b) show an alternative example non-limiting configurationfor reducing voltage. In this example, the optocoupler includes twolight emitting regions 18 which are connected to two blocking regions 19which are connected to a single photovoltaic region 20, in a verticallystacked configuration. Each light emitting region 18 contains anoptional reflector 21 to improve the coupling efficiency of photons tothe photovoltaic region 20. As before, the bandgap of the lowest energyabsorber layer in the solar cell sections should be equal to or lessthan the bandgap of the light emitting section governing the peakemission wavelength. The light emitting region 18 contains two terminals22, 23 and, in this example, two light emitting devices connected inelectrical series. The photovoltaic region 20 contains two terminals 24,25 and one photovoltaic device. When the bandgap energy of the lightemitting and photovoltaic devices are similar, the input voltagesbetween terminals 22, 23 is roughly a factor of two or more greater thanthe voltage between terminals 24, 25.

In the case that the bandgap of the light emitting regions 18 and thephotovoltaic regions 20 of the devices in FIGS. 8-10 are equal, inprinciple the optocoupler can operate also as a voltage increasingdevice. This is achieved by operating the PV section as a light emitterand the light emitter region as a photovoltaic. However, to achieve highpower transfer efficiency, it is often advantageous to optimize thelayer structure to perform for either one of step-up or step-downoperations.

FIG. 10(a) shows an example configuration for the device as a voltageincreasing device. Here a single light emitting region 18 is connectedto a blocking region 19. The blocking region is connected to aphotovoltaic region comprising two separate photovoltaic devices 20. Thebandgap of the lowest bandgap absorber layer in the solar cell regionshould be equal to or less than the bandgap of the light emittingsection governing the peak emission wavelength. An optional reflector 21on the light emitting section devices functions to improve the couplingefficiency of photons to the photovoltaic region 20. Thus, the lightemitting region 18 is on the bottom and the photovoltaic regions 20 areon top.

As shown in FIG. 10(b), the light emitting region 18 contains twoterminals 22, 23 and, in this example, comprises a single light emittingdevice. The photovoltaic region 20 contains two terminals 24, 25 andcomprises two photovoltaic devices connected in electrical series. Whenthe bandgap energy of the light emitting and photovoltaic devices aresimilar, the output voltages between terminals 24, 25 is roughly afactor of two greater than the voltage between terminals 22, 23. Anoptional reflector 26 on the photovoltaic region device functions toimprove the absorption probability of photons emitted from the lightemitting region 18 in the photovoltaic region 20. The example in FIG. 10contains a single light emitting device large enough to provide photonsto both devices in the photovoltaic region 20. Alternatively, anequivalent scheme could use two light emitting devices connected inparallel, as shown in FIG. 11.

FIG. 12 shows an alternative method for increasing voltage. In thisexample, the optocoupler includes two photovoltaic regions 20 which areconnected to two blocking regions 19 which are connected to a singlelight emitting region 18. Each photovoltaic region contains an optionalreflector 26 to improve the coupling efficiency of photons to thephotovoltaic region 20.

As before, the bandgap of the lowest energy absorber layer in the solarcell sections should be equal to or less than the bandgap of the lightemitting section governing the peak emission wavelength. The lightemitting region 18 contains two terminals 22, 23 and, in this example,comprises a single light emitting device. The photovoltaic region 20contains two terminals 24, 25 and comprises two photovoltaic devicesconnected in electrical series.

When the bandgap energy of the light emitting and photovoltaic devicesare similar, the output voltages between terminals 24, 25 is roughly afactor of two or more greater than the voltage between terminals 22, 23.The design can be easily adapted to providing greater voltage steps byusing multijunction photovoltaic devices in the photovoltaic region 20.For example, the photovoltaic devices could each contain two npjunctions separated by tunnel junctions, where the separate junctionsare designed to produce similar photocurrent under illumination from thephotons emitted by the light emitting region. In FIG. 12, the collectionof LED emission is extremely good, as light escaping from the upper andlower surfaces of the LED 18 will end up reaching a PV device. Whencompares this to using a reflector on the LED to boost the probabilityof absorption in the PV device, as in FIGS. 7, 8, even the bestreflector will not achieve close to 100% reflection over all angles, sosome loss is inevitable. This is probably the highest potentialefficiency version of the optocoupler.

FIG. 13 shows another example non-limiting example structure for amonolithic optocoupler. In FIG. 13, the components are arrangedvertically with respect to one another, i.e., with one on top of anotherand tapered so that each component is slightly smaller. This examplecontains one light emitting section 18 and one photovoltaic section 20.The light emitting section 18 has a p-n junction or p-i-n junction diodestructure. The polarity of the n and p materials may be in either inn-on-p or p-on-n geometry. The light emitting section may consist ofbulk semiconductors, such as Al_(x)Ga_(1-x)As or In_(x)Ga_(1-x)P, in anycombination of homojunction or heterojunction architectures. A regionwith dissimilar composition may be employed close to or within the p-njunction region, or in an intrinsic region for p-i-n structures. Thisdissimilar region may consist of a material with different bandgap tothe surrounding semiconductors, or a low dimensional semiconductor suchas single or multi-quantum wells, quantum dots or a superlatticestructure. The n and p layers of the light emitter junction may containwider bandgap outer cladding layers.

A high impedance blocking region 19 is situated between the lightemitting section and PV section. This should be composed ofsemiconductors with a bandgap wide enough to ensure high transmissionprobability of photons generated in the light emitter region. Thestructure may have one or more resistive semiconductor layers with lowelectrically active doping concentration, or one or more di odes formedby p-n or p-i-n junctions.

The photovoltaic region 20 has a p-n junction or p-i-n junction. Thedevice may include bulk semiconductors, such as Al_(x)Ga_(1-x)As orIn_(x)Ga_(1-x)P, in any combination of homojunction or heterojunctionarchitectures. A region with dissimilar composition may be employedclose to or within the p-n junction region, or in an intrinsic regionfor p-i-n structures. This dissimilar region may consist of a materialwith different bandgap to the surrounding semiconductors, or a lowdimensional semiconductor such as single or multi-quantum wells, quantumdots or a superlattice structure. The photovoltaic device will containone or more semiconductor layers with bandgap equal to or less than thebandgap of the layers responsible for the emission in the light emittingsection, and therefore able to absorb the emitted photons. The n and players of the PV junction may contain wider bandgap outer claddinglayers.

A highly doped semiconductor region 31 is positioned between thereflector 21 and the LED 18, between the LED 18 and the blocking layer19, between the blocking layer 19 and the photovoltaic layer 20, betweenthe PV layer 20 and the high resistance region 32, as shown. The lightemitter region 18 and cladding is surrounded by highly dopedsemiconductor regions 31 having one or more layers, used to form ohmiccontact with metals. The highly doped semiconductors should have abandgap wide enough to ensure high transmission probability of photonsgenerated in the light emitter region. Two metal contact structures 27,28 contact the highly doped semiconductor layer 31 surrounding the lightemitting section to form the two electrical terminals of the lightemitting region. An optional reflector 21 on the light emitting sectiondevices functions to improve the coupling efficiency of photons to thephotovoltaic region 20. The reflector may form part of the ohmic contact27 to the light emitting device, or be a separate structure not formingan electrical connection.

The photovoltaic region 20 and any cladding layers are surrounded byhighly doped semiconductor regions 31 having one or more highly dopedsemiconductor layers are used to form ohmic contact with metals. Thisshould have a bandgap wide enough to ensure high transmissionprobability of photons generated in the light emitter region. Two metalcontact structures 29, 30 contact the highly doped semiconductor regions31 surrounding the photovoltaic region to form the two electricalterminals of the photovoltaic region 20.

An optional, additional high resistance region 32 containing one or moreresistive semiconductor layers with low electrically active dopingconcentration, or one or more diodes formed by p-n or p-i-n junctions,may be included below the PV region. This creates electrical isolationbetween adjacent die on the same substrate, if required. Alternatively,the die may be grown on an insulating substrate, or diced into separatecomponents to achieve electrical isolation, if required. If grown on aconducting substrate 33, electrical contact to the photovoltaic region20 may be made through a metal contact connected to the rear side of thesubstrate 34. A highly reflective mirror 26 may be included below the PVsection of the device to improve the probability of absorption in thatsection.

One or more tunnel junctions may be included in the device to improvethe electrical resistance in ohmic contact layers. The tunnel junctionlayers could be positioned between an ohmic contact layer and a PV orLED section of the device, with the purpose of changing the polarity ofthe ohmic contact layer to enable lower series resistance operation.

FIG. 14 shows an alternative device structure for a monolithicoptocoupler having a side-by-side horizontal configuration as in FIG.13. This example contains one light emitting section 18 and twophotovoltaic sections 20 each with the same basic structure as thosedescribed in FIG. 13. A high impedance blocking region 19 is situatedbetween each light emitting section and PV section. The light emitterregion 18 and cladding is surrounded by highly doped semiconductorregions 31. Two metal contact structures 27, 28 make contact with thehighly doped semiconductor layer 31 surrounding the light emittingsection to form the two electrical terminals of the light emittingregion. The light emitter regions 20 and cladding are surrounded byhighly doped semiconductor regions 31. Four metal contact structures 29,30, 35, 36 make contact with the highly doped semiconductor layers 31surrounding the two photovoltaic regions. An optional reflector 26 ispositioned above the topmost photovoltaic region. This may be a separatestructure or form the ohmic contact 29 to the topmost photovoltaicregion.

An optional, additional high resistance region 32 containing one or moreresistive semiconductor layers with low electrically active dopingconcentration, or one or more diodes formed by p-n or p-i-n junctions,may be included below the lowermost PV region. This creates electricalisolation between adjacent die on the same substrate, if required.Alternatively, the die may be grown on an insulating substrate, or dicedinto separate components to achieve electrical isolation, if required.If grown on a conducting substrate 33, electrical contact to thephotovoltaic region 20 may be made through a metal contact connected tothe rear side of the substrate 34. A highly reflective mirror 26 may beincluded below the PV section of the device to improve the probabilityof absorption in that section.

As in FIG. 13, one or more tunnel junctions may be included in thedevice to improve the electrical resistance in ohmic contact layers. Thetunnel junction layers could be positioned between an ohmic contactlayer and a PV or LED section of the device, with the purpose ofchanging the polarity of the ohmic contact layer to enable lower seriesresistance operation.

Separate Components

The optical coupling section of the voltage regulator device may also beconstructed using separate components. FIG. 15 shows an example opticalcoupling scheme using separate light emitting and photovoltaiccomponents. The light emitters can include three separate light emittingdevices 37, each with two metal contact structures 27, 28 for makingelectrical contact to the anode and cathode of each device. The lightemitting devices are connected together in some in some combination ofseries and parallel, with two terminals 22, 23 (one connected to thetransistor 1 and the other to ground). The photovoltaics can have threeseparate photovoltaic devices 38, each with two metal contact structures29, 30 for making electrical contact to the anode and cathode of eachdevice. The photovoltaic devices are connected together in some in somecombination of series and parallel, with two output terminals 24, 25.

The PV and LED components may be bonded together vertically using anadhesive 39, a direct Van der Waals bond or some other semiconductorbonding approach. Alternatively, the devices may be in close verticalproximity but not in intimate contact. The surfaces of the LED and PVdevices may have suitable coatings applied to reduce reflection losses.The example in FIG. 15 contains three LED devices in parallel and 3 PVdevices in series but can contain any number of photovoltaic and lightemitting devices in any combination of series/parallel interconnection.In the embodiment shown, the light emitting devices 37 are stackedvertically on top of the photovoltaic devices 38.

As an alternative to FIG. 15, several photovoltaic or light emittingdevices may be replaced by one large photovoltaic or light emittingdevice. For example, FIG. 16 shows one large photovoltaic device (40)replacing three parallel connected photovoltaics in FIG. 15. The opticalcoupling may also be between adjacent devices with horizontal photontransfer. In FIG. 17, the light emitters comprise three separate lightemitting devices 37, each with two metal contact structures 27, 28 formaking electrical contact to the anode and cathode of each device. Thelight emitting devices are connected together in some in somecombination of series and parallel, with two terminals 22, 23. The PVdevices are in close proximity to the light emitting devices and photonsfrom the LED device are passed to one or more PV devices via emissionfrom the edge of the LED mesa. The photovoltaics comprise three separatephotovoltaic devices 38, each with two metal contact structures 29, 30for making electrical contact to the anode and cathode of each device.The photovoltaic devices are connected together in some in somecombination of series and parallel, with two terminals 24, 25. The LEDand PV mesas may be encapsulated in a material transparent to the LEDemission wavelength, or unencapsulated. Series and parallel connectionscan then be formed by connecting the terminals of the PV and LED devicesin arbitrary series/parallel combinations. An example with three LEDdevices in parallel and 3 PV devices in series is shown in FIG. 17.

The LEDs 8, 18 are in close proximity to the PV devices 9, 20,respectively. There is no strict limit on how far they can be, butgenerally as close as possible would work best for efficient opticalcoupling, as the light from the LEDs is diverging and the PV device isrequired to capture as much of the LED light as possible. A greaterseparation is desirable for galvanic isolation. A typical verticalconfiguration would range from direct and intimate contact to as far asseveral mm of separation.

It is further noted that the description and claims use severalgeometric or relational terms, such as rectangular, series,side-by-side, vertical, horizontal, parallel, and flat. In addition, thedescription and claims use several directional or positioning terms andthe like, such as top and bottom. Those terms are merely for convenienceto facilitate the description based on the embodiments shown in thefigures. Those terms are not intended to limit the invention. Thus, itshould be recognized that the invention can be described in other wayswithout those geometric, relational, directional or positioning terms.In addition, the geometric or relational terms may not be exact. Forinstance, walls may not be exactly parallel to one another but still beconsidered to be substantially parallel because of, for example,roughness of surfaces, tolerances allowed in manufacturing, etc. And,other suitable geometries and relationships can be provided withoutdeparting from the spirit and scope of the invention.

FIGURE NUMBERS

-   -   1. Transistor    -   2. Input voltage terminal    -   3. Output voltage terminal    -   4. Voltage reference    -   5. Error amplifier    -   6. Potential divider resistor 1    -   7. Potential divider resistor 2    -   8. Light emitting section    -   9. Photovoltaic section    -   10. Photon path    -   11. Pnp transistor    -   12. 2^(nd) transistor    -   13. Phototransistor    -   14. Light emitting device    -   15. Pnp phototransistor    -   16. Conventional linear voltage regulator    -   17. Switch    -   18. Light emitting section    -   19. Blocking section    -   20. Photovoltaic section    -   21. Light emitter Reflector    -   22. Light emitter section terminal 1    -   23. Light emitter section terminal 2    -   24. Photovoltaic section terminal 1    -   25. Photovoltaic section terminal 2    -   26. Optional PV reflector    -   27. Light emitter 1^(st) contact metal    -   28. Light emitter 2^(nd) contact metal    -   29. Photovoltaic 1^(st) contact metal    -   30. Photovoltaic 2^(nd) contact metal    -   31. Highly doped semiconductor contact layer    -   32. Optional blocking section    -   33. Substrate    -   34. Optional substrate contact    -   35. Photovoltaic section 3^(rd) contact metal    -   36. Photovoltaic section 4^(th) contact metal    -   37. Separate light emitting device    -   38. Separate photovoltaic device    -   39. Interface layer (adhesive)    -   40. Single large area photovoltaic device

It is noted that the statements made with respect to one embodimentapply to the other embodiments, unless otherwise specifically noted. Forexample, the statements regarding FIG. 1 with respect to configurationand operation apply equally to the embodiments of FIGS. 2-6 and also7-17, and the statements made with respect to FIG. 7 apply to theembodiments of FIGS. 1-6 and also 8-17. It is further understood thatthe description and scope of invention apply equally (though thedescriptions have not been repeated) for each structure that is the sameor similar between each of the various embodiment, and whether or notthose structures have been assigned a similar reference numeral.

The foregoing description and drawings should be considered asillustrative only of the principles of the invention. The invention maybe configured in a variety of manners and is not intended to be limitedby the embodiment. Numerous applications of the invention will readilyoccur to those skilled in the art. Therefore, it is not desired to limitthe invention to the specific examples disclosed or the exactconstruction and operation shown and described. Rather, all suitablemodifications and equivalents may be resorted to, falling within thescope of the invention.

The invention claimed is:
 1. A linear voltage regulator, comprising: aninput terminal for receiving an input voltage; a reference voltageterminal for receiving a reference voltage; an output terminal foroutputting a regulated output voltage; a photovoltaic section having aninput electrically coupled to the input terminal and an outputelectrically coupled to the output terminal; a light emitting sectionthat transmits photons to the photovoltaic section; a potential divider,electrically coupled to the output terminal, that outputs a feedbackvoltage that is proportional to the regulated output voltage; atransistor that provides a fraction of the input voltage to the lightemitting section; and an error amplifier that compares the feedbackvoltage to the reference voltage and minimizes the difference betweenthe reference voltage and the feedback voltage by controlling thefraction of the input voltage provided to the light emitting section bythe transistor.
 2. The linear voltage regulator of claim 1, wherein theinput terminal is electrically coupled to the output terminal via alinear regulator.
 3. The linear voltage regulator of claim 2, whereinthe input of the photovoltaic section is electrically coupled to theinput terminal via a switch that selectively connects the input terminalto the linear regulator.
 4. The linear voltage regulator of claim 3,wherein the switch, selectively connects the input terminal to the inputof the photovoltaic section.
 5. The linear voltage regulator of claim 1,further comprising: a reflector coupling the photons from the lightemitting section to the photovoltaic section.
 6. The linear voltageregulator of claim 5, wherein the reflector is positioned at the lightemitting section or the photovoltaic section.
 7. The linear voltageregulator of claim 1, the the light emitting section comprising one ormore emitting devices and the photovoltaic section comprising first andsecond photovoltaic devices sandwiching at least one of the one or morelight emitting devices.
 8. The linear voltage regulator of claim 1, thephotovoltaic section comprising an array of a plurality of lightemitting devices.
 9. The linear voltage regulator of claim 8, thephotovoltaic section comprising an array of a plurality of photovoltaicdevices, each photovoltaic device being aligned with at least one of theplurality of light emitting devices.
 10. The linear voltage regulator ofclaim 1, wherein the photovoltaic section and the light emitting sectioncomprise discrete components or monolithically connected devices. 11.The linear voltage regulator of claim 1, the photovoltaic section andthe light emitting section comprising a stack of at least one monolithiclight emitting device and at least one monolithic photovoltaic deviceconnected by an electrically isolating layer transparent to a wavelengthof the photons.
 12. The linear voltage regulator of claim 11, whereinthe at least one monolithic light emitting device comprises a diode. 13.The linear voltage regulator of claim 1, the light emitting sectioncomprising a plurality of monolithic light emitting devices connected inseries and/or in parallel and the photovoltaic section comprising aplurality of monolithic photovoltaic devices connected in series and/orin parallel.
 14. The linear voltage regulator of claim 13, furthercomprising a plurality of electrically isolating layers, eachelectrically coupled to and being between one of the plurality ofmonolithic light emitting devices and one of the plurality of monolithicphotovoltaic devices.
 15. A linear voltage regulator comprising: aninput terminal for receiving an input voltage; a reference voltageterminal for receiving a reference voltage; an output terminal foroutputting a regulated output voltage; a photovoltaic sectionelectrically coupled to the output terminal; a light emitting sectionthat transmits photons to the photovoltaic section; a potential divider,electrically coupled to the output terminal, that outputs a feedbackvoltage that is proportional to the regulated output voltage; one ormore transistors that provide a fraction of the input voltage to thelight emitting section, wherein at least one of the one or moretransistors is a phototransistor such that the linear voltage regulatorprovides galvanic isolation between the input terminal and the outputterminal; and an error amplifier that compares the feedback voltage tothe reference voltage and minimizes the difference between the referencevoltage and the feedback voltage by controlling the fraction of theinput voltage provided to the light emitting section by the one or moretransistors.
 16. The linear voltage regulator of claim 15, wherein theone or more transistors comprises a phototransistor that provides afraction of the input voltage to the light emitting section in responseto a control light emitting device electrically coupled to the output ofthe error amplifier.
 17. The linear voltage regulator of claim 15,wherein the one or more transistors comprises a first transistor thatprovides a fraction of the input voltage to the light emitting sectionin response to a second transistor, wherein the second transistor is aphototransistor controlled by a control light emitting deviceelectrically coupled to the output of the error amplifier.